docs: def rosen_nesterov(self, x, rho=100):
          """needs exponential number of steps in a non-increasing f-sequence.
  
          x_0 = (-1,1,...,1)
          See Jarre (2011) "On Nesterov's Smooth Chebyshev-Rosenbrock Function"
  
          """
          f = 0.25 * (x[0] - 1)**2
          f += rho * sum((x[1:] - 2 * x[:-1]**2 + 1)**2)
          return f